Composite products comprising a metal matrix and a reinforcing phase such as ceramic particulates, show great promise for a variety of applications because they combine the stiffness and wear resistance of the reinforcing phase with the ductility and toughness of the metal matrix.
Various metallurgical processes have been described for the fabrication of aluminum matrix composites. These methods are, for instance, based on powder metallurgy techniques and liquid metal infiltration techniques which make use of pressure casting, vacuum casting, stirring and wetting agents. Pressure Infiltration Casting as described in U.S. Pat. No. 5,111,871 by Arnold J. Cook and entitled "Method of Vacuum Casting" describes pressure casting apparatus whereby the mold, metal and heating means are contained within a pressure vessel. The described method for casting essentially comprises the steps of evacuating the pressure vessel while melting the metal within a crucible. The mold, which has a snorkel, is disposed on top of the crucible. The molten metal is fluidically connected to the mold by disposing the snorkel in the crucible of molten metal, thereby isolating the inside of the mold from the interior of pressure vessel. Inert pressurized gas is then used to force the molten metal into the mold. This method necessitates separate steps for melting the metal and fluidically isolating the inside of the mold from the interior of the pressure vessel. Further, a mechanical apparatus, such as a crucible lifter, is needed to connect the snorkel and melted metal before pressurization.
An improvement of this process and apparatus is described in the present invention whereby solid metal is disposed in a chamber on top of the mold. A passage fluidically connects this chamber to the inside of the mold. As the metal is melted, the molten metal covers the passage thereby fluidically isolating the inside of the mold from the interior of the vessel in one step.